Spark ignition engine control with exhaust manifold pressure sensor

ABSTRACT

Control of a spark ignited internal combustion in response to an exhaust manifold pressure measurement of an engine is disclosed. An engine out NOx amount for at least one cylinder is determined at least in part in response to the exhaust manifold pressure measurement and a brake mean effective pressure of the at least one cylinder. An operating condition of the engine is adjusted in response to the engine out NOx amount.

CROSS-REFERENCE TO RELATED APPLICATIONS:

The present application is a divisional of U.S. application Ser. No.15/351,721 filed on Nov. 15, 2016, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to spark ignited engines, andmore particularly is concerned with NOx estimation and control of sparkignited engine operations in response to exhaust manifold pressureoutputs from an exhaust manifold pressure sensor.

BACKGROUND

A spark ignited engine can employ NOx feedback to control spark timing,lambda, and/or air-fuel ratio (AFR) in the engine cylinders. Typically aphysical NOx sensor that measures engine-out NOx is used on mostapplications. However, for certain applications, such as those thatemploy an aggressive fuel, such as type D fuel, the NOx sensor has avery short useful life and is not recommended or desirable for use.

One alternative method to employing a physical NOx sensor involvesdetermining NOx with a “virtual” NOx sensor. One virtual NOx sensortechnique involves a torque over boost (TOB) determination for NOxestimation. One example of TOB NOx estimation is provided in U.S. Pat.No. 5,949,146, which is incorporated herein by reference.

TOB is determined by the brake mean effective pressure (BMEP) (or torqueoutput or braking power of the engine) times the ratio of the intakemanifold temperature (IMT) to the intake manifold pressure (IMP).However, TOB NOx estimation may not provide the desired accuracy orrobustness for the control system to provide the desired systemperformance, particularly as NOx limits decrease. For example, asengine-out limits decrease, the uncertainty in the estimation in theengine out NOx amount may result in operating condition adjustments thatcause an engine out NOx amount occurring that is lower than a thresholdamount, resulting in a lambda below a lean limit and high coefficient ofvariation (COV) of cylinder gross indicated mean effective pressure(GIMEP) and misfire.

Other methods for controlling emissions targets and engine operations,such as those that employ targeting an air-fuel ratio or lambda, alsosuffer from deficiencies due to various conditions such as variation infuel composition, fuel quality, and humidity, and also due to sensordrift error and sensor condition deterioration over time. In addition,pumping mean effective pressure (PMEP) estimates employed in enginecontrols that are made without an exhaust manifold pressure sensorsuffer from uncertainties due to waste gate position, variable geometryturbine inlet position, and variable valve timing and cam phaserposition. Thus, there remains a need for additional improvements insystems and methods for NOx estimation and in the control spark ignitedengine operations.

SUMMARY

Unique systems, methods and apparatus are disclosed for controllingoperation of a spark ignited internal combustion in response to anexhaust manifold pressure measurement of the engine. In one embodiment,an engine out NOx amount for at least one cylinder is determined atleast in part in response to the exhaust manifold pressure measurementand a BMEP of the at least one cylinder. An operating condition of theengine is adjusted in response to the engine out NOx amount.

In another embodiment, the exhaust manifold pressure determination isemployed to determine a mass charge flow which approximates trapped airmass in the at least one cylinder, and a traditional TOB determinationof the engine out NOx amount is modified by replacing the IMP and IMTinputs in the TOB determination with the mass charge flow to estimatethe engine out NOx amount in response to a ratio of the BMEP to the masscharge flow, and also in response to the exhaust manifold pressure andthe spark timing.

This summary is provided to introduce a selection of concepts that arefurther described below in the illustrative embodiments. This summary isnot intended to identify key or essential features of the claimedsubject matter, nor is it intended to be used as an aid in limiting thescope of the claimed subject matter. Further embodiments, forms,objects, features, advantages, aspects, and benefits shall becomeapparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a portion of an internalcombustion engine system with an exhaust manifold pressure sensor.

FIG. 2 is a schematic illustration of a cylinder of the internalcombustion engine system of FIG. 1.

FIG. 3 is a flow diagram of an example procedure for controllingoperation of the internal combustion engine in response to exhaustmanifold pressure.

FIG. 4 is a schematic illustration of a controller apparatus.

FIG. 5 is a flow diagram of another embodiment procedure for controllingoperation of the internal combustion engine in response to exhaustmanifold pressure.

FIG. 6 is a flow diagram of other embodiment procedures for controllingoperation of the internal combustion engine in response to exhaustmanifold pressure.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, any alterations and further modificationsin the illustrated embodiments, and any further applications of theprinciples of the invention as illustrated therein as would normallyoccur to one skilled in the art to which the invention relates arecontemplated herein.

With reference to FIG. 1, an internal combustion engine system 20 isillustrated in schematic form. A fueling system 21 is also shown inschematic form that is operable with internal combustion engine system20 to provide fueling for engine 30 from a first fuel source 102. In oneembodiment, only one fuel source 102 is provided and fuel source 102 islocated so that the fuel is pre-mixed with the charge flow upstream ofthe combustion chambers of engine cylinders. In another embodiment, thefuel from first fuel source 102 is injected directly into thecylinder(s) via direct injection or via port injection. In yet anotherembodiment, fueling system 21 includes an optional second fuel source104 for also providing fueling, and internal combustion engine system 20is a dual fuel system.

Internal combustion engine system 20 includes engine 30 connected withan intake system 22 for providing a charge flow to engine 30 and anexhaust system 24 for output of exhaust gases in an exhaust flow. Incertain embodiments, the engine 30 includes a spark ignited internalcombustion engine in which a gaseous fuel flow is pre-mixed with thecharge flow from first fuel source 102. The gaseous fuel can be, forexample, natural gas, bio-gas, methane, propane, ethanol, producer gas,field gas, liquefied natural gas, compressed natural gas, or landfillgas.

In another embodiment, engine 30 includes a lean combustion engine suchas a diesel cycle engine that uses a liquid fuel in second fuel source104 such as diesel fuel as the sole fuel source, or in combination witha gaseous fuel in first fuel source 102 such as natural gas. However,other types of liquid and gaseous fuels are not precluded, such as anysuitable liquid fuel and gaseous fuel. In the illustrated embodiment,the engine 30 includes six cylinders 34 a-34 f in a two cylinder bank 36a, 36 b arrangement. However, the number of cylinders (collectivelyreferred to as cylinders 34) may be any number, and the arrangement ofcylinders 34 unless noted otherwise may be any arrangement including anin-line arrangement, and is not limited to the number and arrangementshown in FIG. 1.

Engine 30 includes an engine block 32 that at least partially definesthe cylinders 34. A plurality of pistons, such as piston 70 shown inFIG. 2, may be slidably disposed within respective cylinders 34 toreciprocate between a top-dead-center position and a bottom-dead-centerposition while rotating a crankshaft 78. Each of the cylinders 34, itsrespective piston 70, and the cylinder head 72 form a combustion chamber74. One or more intake valves, such an intake valve 92, and one or moreexhaust valves, such as exhaust valve 94, are moved between open andclosed positions by a conventional valve control system, cam phaser, ora variable valve timing system, to control the flow of intake air orair/fuel mixture into, and exhaust gases out of, the cylinder 34,respectively.

FIG. 2 shows a single engine cylinder 34 of the multi-cylinderreciprocating piston type engine shown in FIG. 1. The control system ofthe present invention could be used to control fuel delivery andcombustion in an engine having only a single cylinder or any number ofcylinders, for example, a four, six, eight or twelve cylinder or moreinternal combustion engine. In addition, control system may be adaptedfor use on any internal combustion engine having compression, combustionand expansion events, including a rotary engine, two stroke cycleengines, four stroke cycle engines, N stroke cycle engines, HCCI engine,PCCI engines, and a free piston engine. In other embodiments system 20includes a motor/generator and an energy storage system configured toprovide hybrid operations in which power is selectively provided by theengine, the energy storage system and motor/generator, and combinationsof these. The control system of the present invention may also beemployed with any suitable ignition system, including spark plug 80,diesel pilot ignition, plasma, laser, passive or fuel fed pre-chamber,and integrated pre-chamber spark plug ignition systems, for example.

The control system may further include a cylinder sensor 96 for sensingor detecting an engine operating condition indicative of the combustionin combustion chamber 74 and generating a corresponding output signal tocontroller 100. Cylinder sensor 96 permits effective combustion controlcapability by detecting an engine operating condition or parameterdirectly related to, or indicative of, the combustion event in cylinder34 during the compression and/or expansion strokes. For example,cylinder sensor 96 can measure cylinder pressure (average or peak),knock intensity, start of combustion, combustion rate, combustionduration, crank angle at which peak cylinder pressure occurs, combustionevent or heat release placement, effective expansion ratio, a parameterindicative of a centroid of heat release placement, location andstart/end of combustion processes, lambda, and/or an oxygen amount.

In one embodiment, engine 30 is a four stroke engine. That is, for eachcomplete engine combustion cycle (i.e., for every two full crankshaft 78rotations), each piston 74 of each cylinder 34 moves through an intakestroke, a compression stroke, a combustion or power stroke, and anexhaust stroke. Thus, during each complete combustion cycle for thedepicted six cylinder engine, there are six strokes during which air isdrawn into individual combustion chambers 74 from intake supply conduit26 and six strokes during which exhaust gas is supplied to exhaustmanifold 38. As discussed further below, the present invention measuresan exhaust manifold pressure with at least one exhaust manifold pressuresensor 98 at one or more locations in exhaust manifold 38 and determinesan estimate of the NOx output from the one or more cylinders 34 based atleast in part on the exhaust manifold pressure.

The engine 30 includes cylinders 34 connected to the intake system 22 toreceive a charge flow and connected to exhaust system 24 to releaseexhaust gases produced by combustion of the fuel(s). Exhaust system 24may provide exhaust gases to a turbocharger 40, although a turbochargeris not required. In still other embodiments, multiple turbochargers areincluded to provide high pressure and low pressure turbocharging stagesthat compress the intake flow.

Furthermore, exhaust system 24 can be connected to intake system 22 withone or both of a high pressure exhaust gas recirculation (EGR) system 50and a low pressure EGR system 60. EGR systems 50, 60 may include acooler 52, 62 and bypass 54, 64, respectively. In other embodiments, oneor both of EGR systems 50, 60 are not provided. When provided, EGRsystem(s) 50, 60 provide exhaust gas recirculation to engine 30 incertain operating conditions. In any EGR arrangement during at leastcertain operating conditions, at least a portion the exhaust output ofcylinder(s) 34 is recirculated to the engine intake system 22.

In the high pressure EGR system 50, the exhaust gas from the cylinder(s)34 takes off from exhaust system 24 upstream of turbine 42 ofturbocharger 40 and combines with intake flow at a position downstreamof compressor 44 of turbocharger 40 and upstream of an intake manifold28 of engine 30. In the low pressure EGR system 60, the exhaust gas fromthe cylinder(s) 34 a-34 f takes off from exhaust system 24 downstream ofturbine 42 of turbocharger 40 and combines with intake flow at aposition upstream of compressor 44 of turbocharger 40. The recirculatedexhaust gas may combine with the intake gases in a mixer (not shown) ofintake system 22 or by any other arrangement. In certain embodiments,the recirculated exhaust gas returns to the intake manifold 28 directly.In yet another embodiment, the system 20 includes a dedicated EGR loopin which exhaust gas from one or more, but less than all, of cylinders34 is dedicated solely to EGR flow during at least some operatingconditions.

Intake system 22 includes one or more inlet supply conduits 26 connectedto an engine intake manifold 28, which distributes the charge flow tocylinders 34 of engine 30. Exhaust system 24 is also coupled to engine30 with engine exhaust manifold 38. Exhaust system 24 includes anexhaust conduit 46 extending from exhaust manifold 32 to an exhaustvalve. In the illustrated embodiment, exhaust conduit 46 extends toturbine 42 of turbocharger 40. Turbine 42 may include a valve such ascontrollable waste gate 48 or other suitable bypass that is operable toselectively bypass at least a portion of the exhaust flow from turbine42 to reduce boost pressure and engine torque under certain operatingconditions. In another embodiment, turbine 42 is a variable geometryturbine with a size-controllable inlet opening. In another embodiment,the exhaust valve is an exhaust throttle that can be closed or opened.Turbocharger 40 may also include multiple turbochargers. Turbine 42 isconnected via a shaft 43 to compressor 44 that is flow coupled to inletsupply conduit 26.

An aftertreatment system (not shown) can be connected with an outletconduit 66. The aftertreatment system may include, for example,oxidation devices (DOC), particulate removing devices (PF, DPF, CDPF),constituent absorbers or reducers (SCR, AMOX, LNT), reductant systems,and other components if desired. In one embodiment, exhaust conduit 46is flow coupled to exhaust manifold 32, and may also include one or moreintermediate flow passages, conduits or other structures. Exhaustconduit 46 extends to turbine 42 of turbocharger 40.

Compressor 44 receives fresh air flow from intake air supply conduit 23.Fuel source 102 may also be flow coupled at or upstream of the inlet tocompressor 44 which provides a pre-mixed charge flow to cylinders 34.Intake system 22 may further include a compressor bypass (not shown)that connects a downstream or outlet side of compressor 44 to anupstream or inlet side of compressor 44. Inlet supply conduit 26 mayinclude a charge air cooler 56 downstream from compressor 44 and intakethrottle 58. In another embodiment, a charge air cooler 56 is located inthe intake system 22 upstream of intake throttle 58. Charge air cooler56 may be disposed within inlet air supply conduit 26 between engine 30and compressor 44, and embody, for example, an air-to-air heatexchanger, an air-to-liquid heat exchanger, or a combination of both tofacilitate the transfer of thermal energy to or from the flow directedto engine 30.

In operation of internal combustion engine system 20, fresh air issupplied through inlet air supply conduit 23. The fresh air flow orcombined flows can be filtered, unfiltered, and/or conditioned in anyknown manner, either before or after mixing with the EGR flow from EGRsystems 50, 60 when provided. The intake system 22 may includecomponents configured to facilitate or control introduction of thecharge flow to engine 30, and may include intake throttle 58, one ormore compressors 44, and charge air cooler 56. The intake throttle 58may be connected upstream or downstream of compressor 44 via a fluidpassage and configured to regulate a flow of atmospheric air and/orcombined air/EGR flow to engine 30. Compressor 44 may be a fixed orvariable geometry compressor configured to receive air or air and fuelmixture from fuel source 102 and compress the air or combined flow to apredetermined pressure level before engine 30. The charge flow ispressurized with compressor 44 and sent through charge air cooler 56 andsupplied to engine 30 through intake supply conduit 26 to engine intakemanifold 28.

Fuel system 21 is configured to provide either fuelling from a singlefuel source, such as first fuel source 102 or second fuel source 104. Inanother embodiment, dual fuelling of engine 30 from both of fuel sources102, 104 is provided. In one dual fuel embodiment, fuel system 21includes first fuel source 102 and second fuel source 104. First fuelsource 102 is connected to intake system 22 with a mixer or connectionat or adjacent an inlet of compressor 44. Second fuel source 104 isconfigured to provide a flow of liquid fuel to cylinders 34 with one ormore injectors at or near each cylinder. In certain embodiments, thecylinders 34 each include at least one direct injector 76 for deliveringfuel to the combustion chamber 74 thereof from a liquid fuel source,such as second fuel source 104. In addition, at least one or a portinjector at each cylinder or a mixer at an inlet of compressor 44 can beprovided for delivery or induction of fuel from the first fuel source102 with the charge flow delivered to cylinders 34.

A direct injector, as utilized herein, includes any fuel injectiondevice that injects fuel directly into the cylinder volume (combustionchamber), and is capable of delivering fuel into the cylinder volumewhen the intake valve(s) and exhaust valve(s) are closed. The directinjector may be structured to inject fuel at the top of the cylinder orlaterally of the cylinder. In certain embodiments, the direct injectormay be structured to inject fuel into a combustion pre-chamber. Eachcylinder 34, such as the illustrated cylinders 34 in FIG. 2, may includeone or more direct injectors 76 in the duel fuel engine embodiment. Thedirect injectors 76 may be the primary fueling device for liquid fuelsource 104 for the cylinders 34.

A port injector, as utilized herein, includes any fuel injection devicethat injects fuel outside the engine cylinder in the intake manifold toform the air-fuel mixture. The port injector injects the fuel towardsthe intake valve. During the intake stroke, the downwards moving pistondraws in the air/fuel mixture past the open intake valve and into thecombustion chamber. Each cylinder 34 may include one or more portinjectors (not shown). In one embodiment, the port injectors may be theprimary fueling device for first fuel source 102 to the cylinders 34. Inanother embodiment, the first fuel source 102 can be connected to intakesystem 22 with a mixer upstream of intake manifold 28, such as at theinlet or upstream of compressor 44.

In certain dual fuel embodiments, each cylinder 34 includes at least onedirect injector that is capable of providing all of the designed primaryfueling amount from liquid fuel source 104 for the cylinders 34 at anyoperating condition. First fuel source 102 provides a flow of a gaseousfuel to each cylinder 34 through a port injector or a natural gasconnection upstream of intake manifold 28 to provide a second fuel flow(in the dual fuel embodiment) or the sole fuel flow (in a single fuelsource embodiment) to the cylinders 34 to achieve desired operationaloutcomes.

In the dual fuel embodiment, the fueling from the second, liquid fuelsource 104 is controlled to provide the sole fueling at certainoperating conditions of engine 30, and fueling from the first fuelsource 102 is provided to substitute for fueling from the second fuelsource 104 at other operating conditions to provide a dual flow of fuelto engine 30. In the dual fuel embodiments where the first fuel source102 is a gaseous fuel and the second fuel source 104 is a liquid fuel, acontrol system including controller 100 is configured to control theflow of liquid fuel from second fuel source 104 and the flow of gaseousfuel from first fuel source 102 in accordance with engine speed, engineloads, intake manifold pressures, and fuel pressures, for example. Insingle fuel embodiments where the sole fuel source 102 is a gaseousfuel, a control system including controller 100 is configured to controlthe flow of gaseous fuel from first fuel source 102 in accordance withengine speed, engine loads, intake manifold pressures, and fuelpressures, for example. In single fuel embodiments where the sole fuelsource 104 is a liquid fuel, a control system including controller 100is configured to control the flow of liquid fuel from second fuel source104 in accordance with engine speed, engine loads, intake manifoldpressures, and fuel pressures, for example.

One embodiment of system 20 shown in FIG. 2 includes each of thecylinders 34 with a direct injector 76 (in dual fuel embodiment) and/ora spark plug 80, associated with each of the illustrated cylinders 34a-34 f of FIG. 1. Direct injectors 76 are electrically connected withcontroller 100 to receive fueling commands that provide a fuel flow tothe respective cylinder 34 in accordance with a fuel command determinedaccording to engine operating conditions and operator demand byreference to fueling maps, control algorithms, or other fuelingrate/amount determination source stored in controller 100. Spark plugs80 are electrically connected with controller 100 to receive spark orfiring commands that provide a spark in the respective cylinder 34 inaccordance with a spark timing command determined according to engineoperating conditions and operator demand by reference to fueling maps,control algorithms, or other fueling rate/amount determination sourcestored in controller 100.

Each of the direct injectors 76 can be connected to a fuel pump (notshown) that is controllable and operable to provide a flow or fuel fromsecond fuel source 104 to each of the cylinders 34 in a rate, amount andtiming determined by controller 100 that achieves a desired torque andexhaust output from cylinders 34. The fuel flow from first fuel source102 can be provided to an inlet of compressor 44 or to port injector(s)upstream of cylinders 34. A shutoff valve 82 can be provided in fuelline 108 and/or at one or more other locations in fuel system 21 that isconnected to controller 100. The gaseous fuel flow is provided fromfirst fuel source 102 in an amount determined by controller 100 thatachieves a desired torque and exhaust output from cylinders 34.

Controller 100 can be connected to actuators, switches, or other devicesassociated with fuel pump(s), shutoff valve 82, intake throttle 58,waste gate 48 or an inlet to a VGT or an exhaust throttle, spark plugs80, and/or injectors 76 and configured to provide control commandsthereto that regulate the amount, timing and duration of the flows ofthe gaseous and/or liquid fuels to cylinders 34, the charge flow, andthe exhaust flow to provide the desired torque and exhaust output inresponse to an estimated NOx amount based at least in part on themeasured exhaust manifold pressure and a predetermined engine out NOxlimit.

In addition, controller 100 can be connected to physical and/or virtualengine sensor(s) 90 to detect, measure and/or estimate one or moreengine operating conditions outside of cylinders 34 such as IMT, IMP,mass charge flow (MCF), EGR flow, an oxygen amount or lambda in theexhaust, engine speed, engine torque, spark timing, waste gate orturbine inlet position, and other operating conditions. Controller 100can also be connected to exhaust manifold pressure sensor 98 to detector measure an exhaust manifold pressure so that an engine out NOx amountcan be estimated that is determined at least in part in response to theexhaust manifold pressure measured by EMP sensor 98 during operation ofengine 30.

As discussed above, the positioning of each of the actuators, switches,or other devices associated with fuel pump(s), shutoff valve 82, intakethrottle 58, waste gate 48 or an inlet to a VGT or an exhaust throttle,spark plug(s) 80, injector(s) 76, intake and/or intake valve openingmechanisms, cam phasers, etc. can be controlled via control commandsfrom controller 100. In certain embodiments of the systems disclosedherein, controller 100 is structured to perform certain operations tocontrol engine operations and fueling of cylinders 34 with fuelingsystem 21 to provide the desired engine speed, torque outputs, sparktiming, lambda, and other outputs or adjustments in response to theexhaust manifold pressure measurement from EMP sensor 98.

In certain embodiments, the controller 100 forms a portion of aprocessing subsystem including one or more computing devices havingmemory, processing, and communication hardware. The controller 100 maybe a single device or a distributed device, and the functions of thecontroller 100 may be performed by hardware or software. The controller100 may be included within, partially included within, or completelyseparated from an engine controller (not shown). The controller 100 isin communication with any sensor or actuator throughout the systemsdisclosed herein, including through direct communication, communicationover a datalink, and/or through communication with other controllers orportions of the processing subsystem that provide sensor and/or actuatorinformation to the controller 100.

The controller 100 includes stored data values, constants, andfunctions, as well as operating instructions stored on computer readablemedium. Any of the operations of exemplary procedures described hereinmay be performed at least partially by the controller. Other groupingsthat execute similar overall operations are understood within the scopeof the present application. Modules may be implemented in hardwareand/or on one or more computer readable media, and modules may bedistributed across various hardware or computer implemented. Morespecific descriptions of certain embodiments of controller operationsare discussed herein in connection with FIGS. 3 and 5-6. Operationsillustrated are understood to be exemplary only, and operations may becombined or divided, and added or removed, as well as re-ordered inwhole or in part.

Certain operations described herein include operations to interpret ordetermine one or more parameters. Interpreting or determining, asutilized herein, includes receiving values by any method, including atleast receiving values from a datalink or network communication,receiving an electronic signal (e.g., a voltage, frequency, current, orpulse-width modulation (PWM) signal) indicative of the value, receivinga software parameter indicative of the value, reading the value from amemory location on a computer readable medium, receiving the value as arun-time parameter by any means known in the art, and/or by receiving avalue by which the interpreted or determined parameter can becalculated, and/or by referencing a default value that is interpreted ordetermined to be the parameter value.

In one embodiment, controller 100 is configured to perform a procedure300 such as shown in FIG. 3 for operating a virtual engine out NOxsensor. Engine out NOx concentration is directly correlated to adiabaticflame temperature (AFT), which is the temperature of complete combustionproducts in the constant volume combustion process without doing work,no heat transfer, or changes in kinetic or potential energy. The meanin-cylinder AFT can be predicted based on gross power, which can berepresented by GIMEP, and in-cylinder trapped air mass, which can berepresented by the mass charge flow (MCF) and cylinder trapped air mass.In addition, NOx is affected by peak AFT, which is based on the centroidof heat release location. Therefore engine out NOx estimates aredetermined as a function of peak AFT, which is a function of the ratioof GIMEP to MCF, and also the centroid of heat release (which is relatedto combustion or spark timing), as follows:

NOx=f(GIMEP/MCF,centroid)   Equation 1

Procedure 300 uses an EMP measurement from EMP sensor 98 to estimateGIMEP based on a measured or estimated BMEP and PMEP, where PMEP is thedifference between the EMP and IMP. With GIMEP instead of BMEP in theNOx estimation, engine out NOx estimation is more accurate and morerobust to uncertainties caused by waste gate positioning, cam phaserpositioning, exhaust back pressure, turbo degradation, and othercomponent uncertainties and wear since the pressure in the exhaustmanifold is directly measured by EMP sensor 98.

In one embodiment, procedure 300 includes an operation 302 to determineBMEP in response to an indicated torque or horsepower and displacementvolume of engine 30 and to determine net indicated mean effectivepressure (NIMEP). The NIMEP is determined from the sum of BMEP (brakepower) and friction mean effective pressure (FMEP). Since FMEP is afunction of engine power in general, it can be estimated by BMEP, IMPand EMP. Procedure 300 continues at operation 304 to receive an exhaustmanifold pressure measurement input from EMP sensor 98 and estimate PMEPas the difference between the EMP and the IMP. Procedure 300 continuesat operation 306 to determine the GIMEP from the sum of the NIMEP andthe PMEP.

With the determination of GIMEP, procedure 300 continues at operation308 to determine the engine speed and mass charge flow (MCF) andresidual mass from engine sensor(s) 90. Procedure 300 further continuesat operation 310 to estimate an engine out NOx amount for the measuredengine speed based on a ratio of the GIMEP to mass charge flow since NOxis directly correlated to this ratio. Procedure 300 continues atoperation 312 to adjust one or more operating conditions of enginesystem 20 in response to the estimated engine out NOx amount to meet atargeted performance, such as an emissions target.

In addition to providing a more robust virtual sensor estimation ofengine out NOx amount due to basing the determination at least in parton GIMEP, the exhaust manifold pressure measurement from EMP sensor 98also improves the volumetric efficiency calculation that can be used toestimate the mass charge flow. In addition, the EMP changes with theresidual mass charge flow changes, which allows the engine out NOxestimate to account for charge flow temperature effects, diluenteffects, volumetric-efficiency effects, and charge uniformity effects.

Referring to FIG. 4, there is shown one embodiment of a controllerapparatus such as controller 100 which includes a NOx estimation module402 and an operations control module 404. NOx estimation module 402receives an EMP sensor input 406 from EMP sensor 98 and other inputs(virtual and/or physical) 408 from engine sensor(s) 90 and/or cylindersensor(s) 96. NOx estimation module 402 is configured to determine anestimated engine out NOx amount 410 for one or more cylinders 34 inresponse to inputs 406, 408.

In one embodiment, NOx estimation module 402 is configured to determineBMEP in response to an indicated torque or horsepower and displacementvolume, and also to determine NIMEP based on BMEP. NOx estimation module402 also determines PMEP from the EMP input 406 and an IMP input. NOxestimation module 402 also determines the GIMEP from the sum of theNIMEP and the PMEP, and also to determine MCF. The engine out NOx amountis estimated for a determined engine speed based on a ratio of the GIMEPto mass charge flow since NOx is directly correlated to this ratio.Operations control module 404 is configured to receive the engine outNOx amount and output an operating lever adjustment command 412 to meetor maintain an engine operating performance target and/or emissionstarget.

In operation 312 and/or operating lever adjustment command 412, theadjustment in the one or more operating conditions and/or operatinglever adjustment includes, for example, adjusting at least one operatinglever of system 20 associated with one or more of the lambda and sparktiming in order to deliver one or more of a target engine out NOxamount, a target knock margin, a target brake thermal energy (BTE),and/or a target coefficient of variance for the GIMEP. Levers of system20 that effect the engine out NOx amount and that can be controlled inresponse to the estimated engine out NOx amount to meet a NOx targetinclude one or more of IMT, humidity, spark timing, coolant temperature,compression ratio, intake/exhaust valve timing (opening and closing),swirl, lambda, air-fuel ratio, water injection, steam injection andmembranes, for example.

Possible levers of system 20 that can be adjusted in response to theexhaust manifold pressure sensor measurement to control operations ofengine system 20 to meet emissions or other performance targets mayinclude, for example, valves, pumps and/or other actuators that controla fuel flow to cylinders 34 and/or an air flow to cylinders 34. Furtherexample levers includes an intake air throttle position, a waste gateposition, a turbine inlet opening size, a compressor bypass, variablevalve actuator, a cam phaser, a variable valve timing, switching betweenmultiple lift profiles/cams, compression braking, Miller cycling (earlyand/or late intake valve closing), cylinder bank cutout, cylindercutout, intermittent cylinder deactivation, exhaust throttle, sparktiming, IMT regulation, changing displacement of engine, changing numberof strokes in cycle (e.g. 2 stroke vs. 4 stroke), pressure relief valveventing in the intake and/or exhaust, bypassing one or more of thecompressors or turbines in a single stage turbocharger system or twostage turbocharger system or in a multiple turbine system, switchingturbines in and out, and activating electrically activatedturbocharging/supercharging, power-turbine (coupled to crank oralternator), turbo-compounding, exhaust throttle control downstream ofone or more of the turbines, and EGR flow from one or more of adedicated EGR, high pressure EGR loop, low pressure EGR loop, andinternal EGR.

Other inputs 408 in addition to the exhaust manifold pressure sensormeasurement from EMP sensor 98 are also contemplated at operations 302,304 of procedure 300. Examples of other inputs include positions orindicators associated with a target throttle margin, WG, VGT, compressorbypass, VVA, cam phaser, spark timing, lambda, intake throttle, exhaustthrottle, cylinder deactivation of one or more cylinders or cylinderbanks, engine load, engine derate, addition of additional engines,stored power, TOB or NOx target, fuel flow, air flow, charge flow, EGRflow, compression ratio, valve events, fuel composition, waterinjection, IMT, IMP, jacket water temperature, engine speed, variableRPM of a genset, knock, low temperature coolant temperature (includinginlet and outlet temperatures), high temperature coolant temperature(including inlet and outlet temperatures), RPM and RPM error, any errorrelative to target, kW load, combustion feedback, heat release, centroidof heat release, state of charge, EER, combustion rate (peak, etc.),cylinder pressure, peak cylinder pressure (PCP), PCP normalized by IMP,pressure ratio in cylinder, rate of pressure rise, cylinder pressuresensing, RPM based combustion feedback, knock sensor based combustionfeedback, crankshaft twist based feedback, magnetostrictive torquesensors, strain gauge based cylinder pressure measurements, instrumentedhead bolts, instrumented gaskets, instrumented injector/plug hold-downbolts, ionization sensing, optical sensing, grid parallel, breakerstatus, island mode, transient compensation, load pickup, load shedding,compressor surge, engine protection, engine faults, misfire detection,charge pressure (IMP), water flow (for water injection), and any otherengine sensors that quantify the operating condition.

In one embodiment of the procedures disclosed herein and/or ofcontroller 100, the exhaust manifold pressure measurement from EMPsensor 98 is used in conjunction with the virtual sensors disclosedherein to determine an engine out NOx amount, and/or used to adjust theabove described levers to meet a targeted engine performance, includingemissions, power, combustion, knock and efficiency of engine operations.

Another embodiment procedure 500 shown in FIG. 5 in which an engine outNOx amount based on a modified TOB (indicated as TOB′) is determined.Procedure 500 includes an operation 502 where an exhaust pressuremanifold measurement from EMP sensor 98 is determined. Procedure 500further continues at operation 504 to determine a MCF and spark timing.

Traditional TOB includes determining BMEP, IMT, and IMP as inputs toestimate TOB, and engine out NOx is a function of TOB, spark timing (ST)and waste gate position (WG), as follows:

TOB=Brake Power/(IMP/IMT)   Equation 2

NOx=f(TOB,ST,WG)   Equation 3

Brake power can be an output torque from engine 30, such as fromoperating tables, from a kW-load signal from an alternator, or any othersuitable technique. Since EMP is a function of WG, and since MCF is afunction of IMP/IMT, engine speed and volumetric efficiency, thedetermination of engine out NOx with a modified TOB can be improved asfollows:

NOx=f(TOB′,EMP,ST)   Equation 4,

In Equation 4, the IMP/IMT term in Equation 2 is replaced by MCF todetermine TOB′.

Procedure 500 includes an operation 506 to determine an engine out NOxamount from TOB′, EMP and ST. One or more operating levers of enginesystem 20 can then be adjusted as discussed above in response to theengine out NOx amount to adjust an operating condition of engine 30 inresponse to the engine out NOx amount.

In another embodiment of procedures 300, 500, the virtual estimate ofthe engine out NOx amount and the EMP measurement from EMP sensor 98 canbe employed to balance NOx and knock. A NOx target can be achieved byadjusting engine operating levers to obtain different lambdas and sparktimings. The performance of engine system 20 can be optimized byadjusting spark timing as needed to avoid knock conditions while stayingwithin the NOx target.

Another approach of estimating NOx employs a “black box” model. Theblack box model can include, for example, regression equations, maps,neural network model, and other types of information. The black boxmodel takes measurements of GIMEP, IMP, IMT, engine speed, spark timing,and EMP to estimate engine out NOx.

In another embodiment, the throttle margin is targeted with the wastegate position WG. The throttle margin is measured and compared to atarget throttle margin. For a given engine speed and load and engine outNOx amount, there is a target WG that will deliver the desired throttlemargin. This allows BTE to be maximized within the throttle marginrequirements for stability. While this could be employed to meettargeted NOx without an EMP sensor, an EMP measurement from the EMPsensor 98 improves the accuracy of the virtual engine out NOx sensor.

In another embodiment, the systems and methods in which the virtual NOxsensor is included with EMP sensor 98 also includes a physical engineout NOx sensor 99 (FIG. 1). The physical engine out NOx sensor 99 isemployed to determine engine out NOx unless one or more fault conditionsare detected that indicate that the physical engine out NOx measurementis not accurate, such as, for example, the physical engine out NOxsensor 99 being too cold, defective, and/or providing unreasonable orunsteady measurements. In these fault conditions, the virtual NOx sensorwith EMP sensor 98 is used to determine the engine out NOx amount asdiscussed above.

In a further embodiment of the systems and methods disclosed herein,such as shown in FIG. 6, the virtual NOx sensor disclosed herein isemployed for diagnostics/prognostics of physical NOx sensor 99, ofanother virtual NOx sensor, or of engine health. For example, thevirtual NOx sensor is used to diagnose engine health by comparingexpected values to estimated values. In one procedure 600, an engine outNOx amount is determined according to a traditional TOB analysis or froma measured NOx amount at operation 602. At operation 604, the engine outNOx amount is estimated based on exhaust manifold pressure. At operation606 the measured and/or estimated NOx amounts are compared to oneanother and if the engine out NOx amounts differ by more than athreshold amount, a fault can be issued.

In another embodiment of procedure 600, the engine out NOx amount from aphysical NOx sensor 99 and/or from the virtual NOx sensors discussedherein are used to estimate engine torque output at operation 608. Thetorque output of the engine is measured at operation 610. At operation612 the measured and estimated torque outputs are compared to diagnosean engine condition. For example, if the estimated torque output differsfrom the measured torque output by more than a threshold amount, a faultcan be issued.

Other diagnostic procedure embodiments include diagnostics of the wastegate 48 or of a cam phaser using the EMP measurement from EMP sensor 98.For example, a change in position of these components can be expected toproduce a certain change in EMP, and a fault is issued is the actualchange in EMP differs from the expected change in EMP by more than athreshold amount. In another procedure, a change in spark timing isexpected to produce a certain response in EMP at a fixed throttlemargin. If the actual EMP pressure change and expected pressure changediffer by more than a threshold amount, a fault can be issued.

In another embodiment, the estimated engine out NOx amount is determinedand an estimated lambda is compared to a measured lambda (with a lambdasensor). A determination about fuel quality can be made from thedifference between the measured and estimated lambdas, and used toimprove knock control. This determination could also be used to diagnoseone or more fuel mass flow sensors, or improve a fuel mass flowestimate.

In another embodiment procedure, the measured EMP from EMP sensor 98 isused to determine PMEP at a given operating condition and compare it toan expected PMEP value at the operating condition. If the expected andestimated PMEP values differ by more than a threshold amount, a turbodegradation fault may be indicated. The accuracy of this approach couldbe improved with turbo speed sensing. This procedure can also be used toautomatically recalibrate the engine if the turbocharger was changed(for example a different nozzle ring for improved altitude capability).

This measured PMEP determined from EMP sensor 98 and the IMP at thegiven operating condition also provides a way to estimate GIMEP. Withmeasured PMEP from the EMP and IMP, NIMEP is estimated. Since BMEP ismeasured, friction mean effective pressure (FMEP) can be determined. Anincrease in the FMEP over time can provide an indication of operatingissues with engine 30 and an opportunity to determine or predict enginefailures.

Various aspects of the systems and methods disclosed herein arecontemplated. For example, one aspect relates to a method that includesoperating an internal combustion engine system. The engine systemincludes an intake system connected to an engine with a plurality ofcylinders and at least one fuel source operably connected to theinternal combustion engine system to provide a flow of fuel to each ofthe plurality of cylinders. The intake system is coupled to each of theplurality of cylinders to provide a charge flow from the intake systemto a combustion chamber of the respective cylinder. The internalcombustion engine system further includes an exhaust system including anexhaust manifold. The method includes determining a pressure in theexhaust manifold during a combustion cycle associated with at least oneof the plurality of cylinders; determining a BMEP in the exhaustmanifold during the combustion cycle of the at least one of theplurality of cylinders; determining an engine out NOx amount for the atleast one cylinder in response to the pressure in the exhaust manifoldand the BMEP; and adjusting an operating condition of the at least oneengine in response to the engine out NOx amount.

In one embodiment, the method includes determining a GIMEP of the atleast one of the plurality of cylinders in response to the pressure inthe exhaust manifold and the BMEP of the at least one cylinder anddetermining the engine out NOx amount for the at least one cylinder inresponse to the GIMEP. In a refinement of this embodiment, the GIMEP isdetermined in response to a sum of a PMEP and a NIMEP. In a furtherrefinement, the PMEP is determined in response to a differential betweenthe pressure in the exhaust manifold and an intake manifold pressure,and the NIMEP is based on the BMEP. In another refinement of theembodiment, the method includes determining a mass charge flow and aspark timing associated with the least one cylinder, and whereindetermining the engine out NOx amount is based on a ratio of the GIMEPto the mass charge flow and the spark timing.

In another embodiment, the method includes comparing the engine out NOxamount from the at least one cylinder in response to an engine out NOxamount threshold and adjusting the operating condition of the engine toreduce the engine out NOx amount in response to the engine out NOxamount exceeding the engine out NOx amount threshold. In a refinement ofthis embodiment, adjusting the operating condition includes at least oneof the following: opening or closing at least one of an intake throttlein the intake system, a compressor bypass valve in a compressor bypass,a waste gate of a turbine in the exhaust system, and a variable geometryturbine inlet in the exhaust system; and varying a lift profile of atleast one of an intake valve and an exhaust valve of the cylinder.

In another embodiment, adjusting the operating condition includesadjusting a spark timing to avoid a knock condition in the at least onecylinder. In yet another embodiment, the method includes comparing theengine out NOx amount to a measured engine out NOx amount from thephysical NOx sensor and diagnosing a condition of the physical NOxsensor in response to the comparison. In a refinement of thisembodiment, the method includes estimating a torque output of theinternal combustion engine in response to the measured engine out NOxamount; measuring a torque output of the internal combustion engine withat least one engine sensor; comparing the estimated torque output withthe measured torque output; and diagnosing a condition of the internalcombustion engine in response to the comparison.

According to another aspect, a method includes operating an internalcombustion engine system including an intake system connected to anengine with a plurality of cylinders and at least one fuel sourceoperably connected to the internal combustion engine system to provide aflow of fuel to each of the plurality of cylinders. The intake system iscoupled to each of the plurality of cylinders to provide a charge flowfrom the intake system to a combustion chamber of each of the respectivecylinders. The internal combustion engine system further includes anexhaust system with an exhaust manifold. The method further includesdetermining a pressure in the exhaust manifold during a combustion cycleassociated with at least one of the plurality of cylinders; determininga BMEP in the exhaust manifold during the combustion cycle of the atleast one of the plurality of cylinders; determining a mass charge flowand a spark timing associated with the at least one cylinder during thecombustion cycle; determining a modified TOB from a ratio of the BMEP tothe mass charge flow; determining an engine out NOx amount for the atleast one cylinder in response to the modified TOB, the pressure in theexhaust manifold and the spark timing; and adjusting an operatingcondition of the at least one engine in response to the engine out NOxamount.

According to another aspect, a system includes an internal combustionengine including a plurality of cylinders and at least one engine sensorand an exhaust system configured to receive exhaust from the pluralityof cylinders. The exhaust system includes an exhaust manifold pressuresensor in communication with the exhaust from at least one of theplurality of cylinders. The system also includes an intake systemconfigured to direct a charge flow to the plurality of cylinders and afuel system including at least one fuel source operable to provide aflow of fuel to the plurality of cylinders. A controller is connected tothe internal combustion engine, the at least one engine sensor, and theexhaust manifold pressure sensor. The controller is configured toreceive a pressure signal indicative of the exhaust manifold pressureand an engine signal indicative of a BMEP of the at least one cylinderduring a combustion cycle associated with at least one cylinder. Thecontroller is further configured to determine an engine out NOx amountfor the at least one cylinder in response to the pressure in the exhaustmanifold and the BMEP, and adjust an operating condition of the at leastone engine in response to the engine out NOx amount.

In one embodiment, the controller is configured to determine a GIMEP ofthe at least one of the plurality of cylinders in response to thepressure in the exhaust manifold and the BMEP of the at least onecylinder and determine the engine out NOx amount for the at least onecylinder in response to the GIMEP. In a refinement of this embodiment,the controller is configured to determine a mass charge flow and a sparktiming associated with the least one cylinder, and the engine out NOxamount is based on a ratio of the GIMEP to the mass charge flow and thespark timing.

In another embodiment, the fuel is selected from the group consisting ofnatural gas, bio-gas, methane, propane, ethanol, producer gas, fieldgas, liquefied natural gas, compressed natural gas, or landfill gas. Inanother embodiment, the controller is configured to adjust at least oneof the following in response to the engine out NOx amount: a sparktiming in the at least one cylinder in response to the engine out NOxamount and a lambda in the at least one cylinder in response to theengine out NOx amount.

According to another aspect, an apparatus includes an electroniccontroller operatively connected with an internal combustion engine. Theengine includes a plurality of cylinders and is connected to an exhaustmanifold configured to receive exhaust from the plurality of cylindersand an intake system configured to direct a charge flow to the pluralityof cylinders. The electronic controller is also operatively connectedwith an exhaust manifold pressure sensor of the exhaust manifold and afuel system including at least one fuel source operable to provide aflow of fuel into the charge flow to the plurality of cylinders. Theelectronic controller includes a plurality of modules including: a NOxestimation module configured to determine an engine out NOx amount inresponse to an exhaust manifold pressure from the exhaust manifoldpressure sensor and a BMEP of at least one of the plurality of cylindersand an operation control module configured to adjust operations of theinternal combustion engine in response to the engine out NOx amount.

In one embodiment, the NOx estimation module is configured to determinea GIMEP in response to the exhaust manifold pressure and the BMEP. In arefinement of this embodiment, the NOx estimation module is configuredto determine a mass charge flow and a spark timing associated with theleast one cylinder, and the NOx estimation module is further configuredto determine the engine out NOx amount based on a ratio of the GIMEP tothe mass charge flow and the spark timing.

In another embodiment, the operation control module is configured toadjust at least one of adjust a spark timing and a lambda in the atleast one cylinder of the internal combustion engine in response to theengine out NOx amount.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly certain exemplary embodiments have been shown and described. Thoseskilled in the art will appreciate that many modifications are possiblein the example embodiments without materially departing from thisinvention. Accordingly, all such modifications are intended to beincluded within the scope of this disclosure as defined in the followingclaims.

In reading the claims, it is intended that when words such as “a,” “an,”“at least one,” or “at least one portion” are used there is no intentionto limit the claim to only one item unless specifically stated to thecontrary in the claim. When the language “at least a portion” and/or “aportion” is used the item can include a portion and/or the entire itemunless specifically stated to the contrary.

1-10. (canceled)
 11. A method, comprising: operating an internalcombustion engine system, the internal combustion engine systemincluding an intake system operably connected to an internal combustionengine comprising a plurality of cylinders and at least one enginesensor, at least one fuel source operably connected to the internalcombustion engine system and configured to supply a fuel to each of theplurality of cylinders, an exhaust system comprising an exhaust manifoldand an exhaust manifold pressure sensor, and a controller operableconnected to the at least one engine sensor and the exhaust manifoldpressure sensor; determining a pressure in the exhaust manifold during acombustion cycle associated with at least one cylinder of the pluralityof cylinders via the exhaust manifold pressure sensor; determining abrake mean effective pressure (BMEP) in response to the pressure in theexhaust manifold or via the at least one engine sensor during thecombustion cycle; determining a mass charge flow and a spark timingassociated with the at least one cylinder during the combustion cyclevia the determined pressure in the exhaust manifold or via the at leastone engine sensor; determining a modified torque over boost (TOB) from aratio of the determined BMEP to the determined mass charge flow;determining an estimated engine out NOx amount for the at least onecylinder in response to the determined modified TOB, the determinedpressure in the exhaust manifold and the determined spark timing; andadjusting an operating condition of the internal combustion engine inresponse to the determined estimated engine out NOx amount. 12-20.(canceled)
 21. The method of claim 11, further comprising: comparing thedetermined estimated engine out NOx amount from the at least onecylinder to an engine out NOx amount threshold; and wherein theadjusting of the operating condition of the internal combustion engineincludes reducing an engine out NOx amount in response to the determinedestimated engine out NOx amount exceeding the engine out NOx amountthreshold.
 22. The method of claim 21, wherein the adjusting of theoperating condition of the internal combustion engine includes at leastone of: opening or closing at least one of an intake throttle in theintake system, a compressor bypass valve in a compressor bypass, a wastegate of a turbine in the exhaust system, and a variable geometry turbineinlet in the exhaust system; and varying a lift profile of at least oneof an intake valve and an exhaust valve of the at least one cylinder.23. The method of claim 11, further comprising: comparing the determinedestimated engine out NOx amount from the at least one cylinder to ameasured engine out NOx amount from a physical engine out NOx sensor;and diagnosing a condition of the physical engine out NOx sensor inresponse to the comparison of the determined estimated engine out NOxamount and the measured engine out NOx amount.
 24. The method of claim11, further comprising: estimating a torque output of the internalcombustion engine in response to the determined estimated engine out NOxamount; measuring a torque output of the internal combustion engine withvia the least one engine sensor; comparing the estimated torque outputwith the measured torque output; and diagnosing a condition of theinternal combustion engine in response to the comparison of theestimated torque output and the measured torque output.
 25. An apparatusfor operative connection with an internal combustion engine including aplurality of cylinders and least one engine sensor, an exhaust systemcomprising an exhaust manifold and an exhaust manifold pressure sensor,and intake system, and a fuel system including at least one fuel source,wherein the apparatus comprises an electronic controller configured to:determine a pressure in the exhaust manifold via the exhaust manifoldpressure sensor during a combustion cycle associated with at least onecylinder of the plurality of cylinders; determine a brake mean effectivepressure (BMEP) in response to the determined pressure in the exhaustmanifold or via the at least one engine sensor during the combustioncycle; determine a mass charge flow and a spark timing associated withthe at least one cylinder during the combustion cycle via the determinedpressure in the exhaust manifold or via the at least one engine sensor;determine a modified torque over boost (TOB) from a ratio of thedetermined BMEP to the determined mass charge flow; determine anestimated engine out NOx amount for the at least one cylinder inresponse to the determined modified TOB, the determined pressure in theexhaust manifold and the determined spark timing; and adjust anoperating condition of the internal combustion engine in response todetermined the estimated engine out NOx amount.
 26. The apparatus ofclaim 25, wherein the controller is further configured to adjust atleast one of a spark timing and a lambda value in the at least onecylinder of the internal combustion engine in response to the determinedestimated engine out NOx amount.
 27. The apparatus of claim 25, whereinthe controller is further configured to compare the determined estimatedengine out NOx amount from the at least one cylinder to an engine outNOx amount threshold and adjust the operating condition of the internalcombustion engine to reduce an engine out NOx amount in response to thedetermined estimated engine out NOx amount exceeding the engine out NOxamount threshold.
 28. The apparatus of claim 27, wherein the operatingcondition of the internal combustion engine is adjusted by at least oneof: opening or closing at least one of an intake throttle in the intakesystem, a compressor bypass valve in a compressor bypass, a waste gateof a turbine in the exhaust system, and a variable geometry turbineinlet in the exhaust system; and varying a lift profile of at least oneof an intake valve and an exhaust valve of the at least one cylinder.29. The apparatus of claim 25, wherein the controller is furtherconfigured to: compare the determined estimated engine out NOx amount toa measured engine out NOx amount from a physical engine out NOx sensor;and diagnose a condition of the physical engine out NOx sensor inresponse to the comparison of the determined estimated engine out NOxamount and the measured engine out NOx amount.
 30. The apparatus ofclaim 25, wherein the controller is configured to: estimate a torqueoutput of the internal combustion engine in response to the determinedestimated engine out NOx amount; measure a torque output of the internalcombustion engine via the at least one engine sensor; compare theestimated torque output with the measured torque output; and diagnose acondition of the internal combustion engine in response to thecomparison of the estimated torque output and the measured torqueoutput.
 31. A system, comprising: an internal combustion engineincluding a plurality of cylinders and at least one engine sensor; anexhaust system configured to receive exhaust from the plurality ofcylinders, the exhaust system including an exhaust manifold and anexhaust manifold pressure sensor in communication with the exhaustreceived from at least one cylinder of the plurality of cylinders; anintake system configured to direct a mass charge flow to the pluralityof cylinders; a fuel system including at least one fuel source operablyconnected to the internal combustion engine and configured to supply afuel to each of the plurality of cylinders; and a controller operableconnected to the at least one engine sensor and the exhaust manifoldpressure sensor, wherein the controller is connected to receive apressure signal indicative of the exhaust manifold pressure, wherein thecontroller is configured to: determine a brake mean effective pressure(BMEP) in response to the exhaust manifold pressure or via the at leastone engine sensor during a combustion cycle associated with at least onecylinder; determine a mass charge flow and a spark timing associatedwith the at least one cylinder during the combustion cycle in responseto a received signal indicative of the pressure in the exhaust manifoldor via the at least one engine sensor; determine a modified torque overboost (TOB) from a ratio of the determined BMEP to the determined masscharge flow; determine an estimated engine out NOx amount for the atleast one cylinder in response to the determined modified TOB, thepressure in the exhaust manifold and determined the spark timing; andadjust an operating condition of the internal combustion engine inresponse to the determined estimated engine out NOx amount.
 32. Thesystem of claim 31, wherein the fuel is selected from the groupconsisting of natural gas, bio-gas, methane, propane, ethanol, producergas, field gas, liquefied natural gas, compressed natural gas, andlandfill gas.
 33. The system of claim 31, wherein the controller isconfigured to adjust at least one of a spark timing and a lambda valuein the at least one cylinder of the internal combustion engine inresponse to the determined estimated engine out NOx amount.
 34. Thesystem of claim 31, wherein the controller is configured to compare thedetermined estimated engine out NOx amount from the at least onecylinder in response to an engine out NOx amount threshold and adjustthe operating condition of the internal combustion engine to reduce anengine out NOx amount in response to the determined estimated engine outNOx amount exceeding the engine out NOx amount threshold.
 35. The systemof claim 34, wherein the operating condition of the internal combustionengine is adjusted by at least one of: opening or closing at least oneof an intake throttle in the intake system, a compressor bypass valve ina compressor bypass, a waste gate of a turbine in the exhaust system,and a variable geometry turbine inlet in the exhaust system; and varyinga lift profile of at least one of an intake valve and an exhaust valveof the at least one cylinder.
 36. The system of claim 31, furthercomprising: a physical engine out NOx sensor; and wherein the controlleris configured to: compare the determined estimated engine out NOx amountto a measured engine out NOx amount from the physical engine out NOxsensor; and diagnose a condition of the physical engine out NOx sensorin response to the comparison of the determined estimated engine out NOxamount and the measured engine out NOx amount.
 37. The system of claim31, wherein the controller is configured to: estimate a torque output ofthe internal combustion engine in response to the determined estimatedengine out NOx amount; measure a torque output of the internalcombustion engine via the at least one engine sensor; compare theestimated torque output with the measured torque output; and diagnose acondition of the internal combustion engine in response to thecomparison of the estimated torque output and the measured torqueoutput.